1. Field of the Invention
The present invention relates to a method and an engine control unit for detecting combustion misses in part-engine operation in which only some of the cylinders are operated.
2. Description of Related Art
In a certain engine control concept for a combustion engine the cylinders of a combustion engine are subdivided into a plurality of cylinder groups, which are triggered independently of each other. If a lower torque is to be requested in such a combustion engine, it is possible to deactivate one or a plurality of cylinders. Such an operating type is referred to as part-engine operation. If half of the cylinders are deactivated, then this is referred to as half-engine operation. In one type of half-engine operation, the deactivation of the one half of the cylinders is implemented by deactivating the intake and discharge valves as well as the injection (HEO). As an alternative, another type of half-engine operation may also be realized solely by deactivation of the injection (HEOIVD), which means that air is pumped through the cylinders, so that the following converter is no longer able to convert at λ=1. For this reason, HEOIVD is realized only in the configuration of a bank suppression since one exhaust-gas bank will then always be activated normally and completely. In half-engine operation, all cylinders are then blanked out (deactivated) on the second exhaust-gas bank.
Legal provisions in the U.S. and in Europe require the detection of non-combusting cylinders (cut-outs). Conventional methods for this purpose consist of monitoring irregular running, the ion-flow method, analysis of the combustion chamber pressure, or an analysis of the λ value. Monitoring the irregular running is a frequently used method in which the angular acceleration of the crankshaft, which is determined by the read-in and conditioning of the speed sensor signal (pulse-generator wheel), is analyzed. An engine working cycle is subdivided into angle segments and assigned to the particular cylinder that is predominantly responsible for the given angular acceleration. For each angle segment, the pass-through time is determined and corrected via an adaptation algorithm which compensates for the tolerances of the pulse-generator wheel. The corrected segment times may be evaluated with regard to the response with respect to other cylinders or with respect to the own time characteristic.
One central variable used to evaluate the segment times so as to determine combustion misses is the irregular running luts (n) of a segment, which is a function of the difference between the segment times of successive segments.
For the half-engine operation (i.e., for HEO and HEOIVD), the evaluation methods for the segment times or the irregular running calculation must be adapted since extended segment times occur there in the deactivated cylinders for system-related reasons. Without adaptations, the partial diagnoses in the deactivated cylinders may respond and cause unfounded fault memory entries.